1. Technical Field of the Invention
This disclosure relates generally to a structure of a pressure control reservoir with a check valve through which a brake fluid flows to a wheel cylinder (W/C) in a brake fluid pressure control mode, for example, in an antilock brake system (ABS).
2. Background Art
Japanese Patent No. 2670340 teaches a brake system for automotive vehicles which is equipped with a pressure control reservoir (also called a switch reservoir). The pressure control reservoir works to store brake fluid, as drained from wheel cylinders, in an ABS (Antilock Brake System) control mode, to control increasing of pressure in the wheel cylinders to avoid skidding of the wheels. The pressure control reservoir is also coupled to a master cylinder (M/C) and works to deliver the brake fluid, as supplied form the master cylinder, to a pump while controlling a difference in pressure between the master cylinder and an inlet of the pump in a traction control mode. The pressure control reservoir is equipped with a check valve of a normally open type which is closed when the pressure in the master cylinder is being increased and opened in the traction control mode. The check valve serves to avoid the exertion of an excessive pressure, as produced by a driver's braking operation in the master cylinder, on the pressure control reservoir and also ensures the stability in supplying the brake fluid to the pump in the traction control mode.
When the driver of the vehicle performs the braking operation to generate a braking force, a piston in the pressure control reservoir needs to be moved to close the check valve before the brakes are actually applied to the wheels. This consumes a volume of the brake fluid required to move the piston in the pressure control reservoir, thus resulting in a lag in start of actual work of the brakes. Specifically, a time lag occurs between the driver's actuation of the brake and the start of actually braking the wheels, which may cause the driver to think that braking the wheel requires more effort on the brake.